Despite intensive preventive efforts over the past several years in hospital and other healthcare facilities, the incidence of life threatening infections caused by a growing array of antibiotic resistant bacteria (sometimes referred to as “superbugs”) has grown significantly and is now posing a serious problem for medical staff worldwide. According to an editorial in the journal “Science” (July 2008), the number of deaths in 2006 attributable to bacterial infections in healthcare facilities in the United States exceeded the U.S. death toll attributed to HIV/AIDS in the same year, and probably result in as many as 70,000 deaths per year in the United States. This is despite the best efforts of healthcare personnel properly to clean their facilities and the equipment contained therein.
The major causative agents (bacteria) for hospital-based infections (nosocomial infections) are Clostridium difficile (C. difficile); E. coli; Pseudomonas aeruginosa; methicillin-resistant Staphylococcus aureus (MRSA); and vancomycin-resistant Enterococcus (VRE).
Approximately 5% of all acute care hospitalizations in the U.S. develop a nosocomial infection with an incidence rate of five infections per thousand patient days, and early estimates of the added expenditure are in excess of $4.5 billion (Wentzel R, Edmond M D, “The Impact of Hospital Acquired Blood Stream Infections,” Emerg. Inf. Dis., March-April 2001:7(174)). A more recent estimate of the aggregate direct hospital cost for nosocomial infections in 2007 (R D Scott, CDC, March 2009) was between $35.7 and $45.0 billion. When this rate is applied to the 35 million patients admitted to 7,000 acute-care institutions in the U.S., it is estimated that there are more than 2 million cases per year. Nosocomial infections are estimated to double, at least, the mortality and morbidity risks of any admitted patient.
The significant, and growing, incidence of antibiotic resistant bacteria in healthcare facilities has been termed by some as a “Silent Epidemic”. On the international scene, a World Health Organization survey of 55 hospitals in 14 countries representing four WHO regions (Europe, Eastern Mediterranean, South-East Asia and Western Pacific) reported that an average of 8.7% of hospital patients had nosocomial infections. The WHO estimates that, at any time, over 1.4 million people worldwide suffer from infection acquired in a hospital.
Of particular concern in this context are the bacteria C. difficile and MRSA. Until recently, C. difficile was relatively uncommon, but has now become epidemic in many regions of the world. Indeed, it is now recognized by a growing number of public health officials as a worldwide epidemic (pandemic) with incalculable financial and health implications. MRSA has been identified by the American Academy of Orthopaedic Surgeons as the single biggest concern for surgical procedures, and concurs with recent journal articles that it constitutes a “silent epidemic.” Under current healthcare facility cleaning and sterilizing procedures, both C. difficile and MRSA, as well as the aforementioned E. coli; Pseudomonas aeruginosa; and vancomycin-resistant Enterococcus (VRE), are ineffectively treated and subsequently removed, so that colonies of these pathogens accumulate in healthcare facilities, especially on porous surfaces such as carpets and drapes.
Attempts to combat and kill nosocomial infections caused by bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus are hampered by the fact that the bacteria grow within biofilms that protect them from adverse environmental factors. A biofilm is an aggregate of microorganisms in which cells adhere to each other and/or to a surface. They are frequently embedded in a self produced matrix of extracellular polymeric substance (EPS), a polymeric conglomeration generally composed of extracellular DNA, proteins and polysaccharides. Biofilms form on surfaces, e.g. in hospital settings, in the presence of water vapor.
Free floating microorganisms in planktonic (single cell) mode attach to a surface, and if not immediately removed, will anchor themselves more permanently to the surface. These first colonists provide more diverse adhesion sites for the arrival of other cells, thus beginning to build a matrix that holds the biofilm together and provides additional anchoring sites for arriving cells. The biofilm grows through a combination of cell division and recruitment. When the biofilm is established, the aggregate cell colonies are apparently increasingly antibiotic resistant. It has also been reported that biofilm bacteria apply chemical weapons to defend themselves against disinfectants and antibiotics (see “Biofilm Bacteria Protect Themselves With Chemical Weapons”, Dr. Carsten Matz et. al., Helmholtz Centre for Infection Research, Brauschweig, reported on Informiac.com, Jul. 23, 2008).
Bacteria living in a biofilm have significantly different properties from the planktonic form of the same species, as the dense and protected environment of the film allows them to co-operate and interact in various ways. Traditional hospital cleaning procedures and solutions are usually not sufficient to eradicate long term contaminations, and one major reason for their persistence seems to be the capability of the bacteria to grow within biofilms that protect them from adverse environmental factors.
Also of growing concern are threatened bioterrorist and warfare attacks using potentially lethal bacteria. Some of the deadliest bacteria, for example anthrax, are highly resistant to conventional sterilization agents and treatments. Contamination of public facilities with such bacteria constitutes a significant threat to human life with residual amounts of such bacteria being almost impossible to remove using current methods.